A light emitting diode (LED) is a semiconductor element for converting electric energy into light. As compared with existing light sources such as a fluorescent lamp, an incandescent lamp, etc., the LED has advantages of low power consumption, a semi-permanent span of life, a rapid response speed, safety and an environment-friendliness. Therefore, many researches are devoted to substitution of the existing conventional light sources with the LED. The LED is now being increasingly used as a light source for lighting devices, for example, various lamps used interiorly and exteriorly, a liquid crystal display device, an electric sign and a street lamp and the like.
Since the fluorescent lamp which is widely used as an indoor lighting device has a limited lifespan, carbonization occurs with the lapse of a certain time, so that the illuminance of the fluorescent lamp is reduced. Then, the lifespan of the fluorescent lamp is rapidly exhausted and the fluorescent lamp should be changed periodically. Therefore, a lot of consequent cost for maintaining and repairing the fluorescent lamp is required and the fluorescent lamp has a high power consumption.